Wednesday, December 22, 2010

FYI before you buy : TOPAZ Colors, cut, treatments, gemology.

"Topaz of any type is a good jewelry stone and it is historically one of the most important gemstones. With its relatively high refractive index and hardness of eight (Mohs scale), with no special sensitivity to chemicals it can be used, with appropriate care (should be protected from hard knocks), in any jewelry application. Topaz is the birthstone for those who are born in the month of November and it comes in many colors, including clear, brown, yellow, orange, red, pink and blue. The blue topaz, with a pale to medium blue color created by irradiation, can be found in very large sizes at affordable prices. The fine golden-yellow variety, known as Imperial Topaz, is relatively scarce. Topaz colors are rarely vivid. The most common color is yellow with a red tint; the most valuable is pink to reddish; the most popular is blue. The coloring agents are iron and chromium.

Blue topaz: Natural blue topaz is rare. Found in all major deposits and also in England (Cornwall), Northern Ireland and Scotland. Most of the blue topazes are enhanced colorless topaz gemstone .

Champagne topaz: One of the very few naturally colored varieties of topaz in a light to medium shade of brown, primarily found in Mexico.

Imperial topaz: The most sought after of all natural topaz. Its rich golden color is generally not enhanced by any kind of treatment. The most important deposit was found in Minas Gerais, Brazil.

Pink topaz: A natural pink topaz is very rare and costly. The vast majority of pink topazes are heat-treated yellow stones that turn pink. The most valuable variety of topaz can be found in Brazil, Pakistan and Russia.

Mystic Topaz : A new high tech enhancement process applied to colorless stones such as topaz and quartz has created a new variety we call "Mystic Topaz."Mystic Topaz displays a stunning rainbow effect that makes it all at once unique, fashionable and different. The color, brilliance and clarity of the final product depend on the quality, cut and polish of the original gemstone. Colorless topaz, the raw basic material, is always untreated. In order to convert eye clean colorless topaz of fine quality into Mystic topaz, a high tech process known as thin film deposition is used. The cut and polished topaz is coated with an extremely thin titanic film. Very little heat is involved in the process that produces the optical effects. The treatment is durable, hard, and only a few microns in thickness. With care, the enhancement will last the life of the jewelry setting.

White Topaz : Colorless topaz is fairly common and is sometimes given a brilliant cut and sold as a substitute for diamond.

Blue topaz begins as colorless or very lightly tinted natural topaz crystals, which are then irradiated to change the color to blue and heated to stabilize the change. Neutron bombardment in a nuclear reactor produces the deep slightly greenish or grayish "London Blue", while electron bombardment in a linear accelerator results in the light aqua-like blue known as "Sky Blue". Combinations of both treatments produce the highly saturated "Swiss" and "Electric" blues. If neutron bombardment has been used, there is residual radioactivity, and the gems must be held, up to a year, before they have "cooled" enough to be worn.

Blue topaz has become one of the top selling gems in the jewelry business, since blue topaz is unusual in offering excellent hardness (8 on the Mohs scale) and brilliance at a very reasonable cost.

Blue topaz can be found in both lighter and darker tones, usually known in the trade as Sky Blue Topaz, Swiss Blue Topaz and London Blue Topaz. As in the case of other blue gems, the more saturated blues tend to have a higher value. So in topaz it is the London Blue that usually regarded as the most valuable. There are two important things to know about blue topaz. The first thing is that while topaz is very hard, it is not the most durable gemstone. That's because it has perfect cleavage, a property it shares with diamond. That means it can be chipped or split by a sharp blow, so it should be protected from hard knocks.

The second important thing is that topaz does not occur naturally in the deeply saturated blues you find in the market today. Blue topaz in nature is very rare indeed, and tends to a very pale blue. The vivid blues available in the market have all been produced by treating white topaz -- first with irradiation, then with heat. The color change is permanent and stable, but recently there has been some controversy about the safety of this treatment for the consumer.

London Blue Topaz is a medium to dark grayish blue, sometimes described as "steely" or "inky." Many London Blues have a slightly greenish tone when viewed from certain angles.

The reason that blue topaz is so reasonably priced is that topaz is a very abundant material. But natural topaz occurs mainly in white (colorless) and brown; natural blue topaz is actually very rare. Virtually all the blue topaz in the market is produced by treating white topaz with radiation.

The reason that the color of topaz can be changed by irradiation is a function of the special way that topaz gets its color. Most gems, such as sapphire, are colored by trace elements such as iron or titanium. Some gems, such as peridot, are colored by elements in their essential chemical composition. But topaz is unique in that the color results from so-called color centers, which are imperfections in the crystal lattice that change the way the crystal absorbs light.

London Blue Topaz is typically produced by exposure to radiation in a nuclear reactor. When topaz is exposed to fast neutrons, the radiation changes the color centers, producing the deep blue color. Subsequent heat treatment is often used to lighten the inky color. Material treated this way is likely to be radioactive and may require several months of storage before the radioactivity decays to safe levels. There are very strict rules in place to protect not only consumers but also the cutters and gem dealers who handle these gems on a daily basis."

The valuable information about Topaz gemology in this article is provided by Gem Select .


Leta Porter said...

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